Power supply with dual asymmetrical inputs

ABSTRACT

A dual asymmetric input power supply architecture for use in power systems employing input power source redundancy. The dual asymmetric input power supply operates from a main input of the power supply when acceptable voltage is present on the main input. If the main input fails or is out of tolerance, power can be supplied from an auxiliary input through a transformer isolated switching converter. The dual asymmetric input power supply architecture maintains the high efficiency of a single-input power supply while providing an auxiliary connection for input power source redundancy.

BACKGROUND

1. Field of the Description

This application relates generally to the field of power systems, andmore particularly to high reliability power systems with redundant powersupply units and/or the capability of operating from more than oneindependent electrical power source.

2. Relevant Background

Power systems for data processing and communications equipment areexpected to provide power to electronic equipment with extremely highreliability. For example, data center power systems may be expected toprovide greater than 99.9%, 99.99%, or even 99.999% availability ofpower for the electronic equipment of the data center. To provide thishigh reliability, these systems typically implement fault-tolerantarchitectures with redundant power paths through redundant power supplyunits and/or the capability of operating from more than one independentelectrical power source.

Redundancy in power supply units may be provided by including additionalpower supply units. For example, power systems typically implement N+1redundancy, meaning that if N power supply units are required to supplythe required output load, the power system includes an additional powersupply unit besides the required N power supply units. In this way, ifany one of the power supply units is out of operation because ofcomponent failure or system maintenance, the power system can stillsupply the rated load.

Power supply unit redundancy can only improve the reliability of thesystem up to the reliability of the single input power source.Therefore, many power systems employ redundancy of input power sources.These systems may have multiple independent primary power sources or aprimary power source and a backup power source such as a generatorand/or battery back-up.

Some fault tolerant power systems use multiple independent alternatingcurrent (AC) input power sources. These systems are expected to operateproperly from both AC input power sources or from either independent ACinput source if the other source fails or is out of tolerance. In somesystems, the output load should be shared between both independent ACinput sources when both sources are present.

Power systems that accept multiple independent power sources mustmaintain isolation between each power source. One reason for powersource isolation is that independent AC and/or direct current (DC) powersources may have differences in the reference point, voltage, frequency,and/or phase from one another. In addition, multiple input power sourcesmust be isolated so that excessive current does not flow between theindependent power sources. For example, a power supply acceptingmultiple independent AC inputs may be required to accept AC voltagesfrom the input sources up to 240 volts and deliver tens of amps ofcurrent to a load without allowing more than a few thousandths of an ampof current to flow between the input sources.

High isolation between independent input sources is also a safetyrequirement. Non-isolated inputs may allow voltage to feed through fromone input source to another input source, which may present anunacceptable safety hazard. For example, when an AC power cord isunplugged from a wall outlet, the prongs of the plug are exposed andeasily touched. Therefore, voltage from other input power sources shouldnot feed through to the exposed prongs of the unplugged AC power cord.

One power system architecture that provides multiple isolated inputsources uses separate single-input power supply units rated for the fullload providing power from each input source. This type of redundancy maybe called N+N redundancy because, if N power supply units are requiredto supply the load from one input power source, N+N power supply unitswould be required to provide the load from two independent input powersources.

Another approach is to use dual-input power supply units with isolatedinput power paths. One type of dual-input power supply converts multipleAC input voltages from independent inputs to an isolated secondary DCvoltage, which may then be combined. This type of dual-input powersupply provides high isolation between inputs without degradingefficiency. However, this type of power supply does not have asignificant advantage over the N+N redundant power system architecturewith regard to cost or system volume.

A second type of dual-input power supply uses transformer isolation ineach input power path within or just following a power factor correctionstage of the power path. This approach avoids duplication of the lowvoltage output conversion circuits but reduces efficiency in each powerpath by about five percent by including two transformers in each inputpower path. Additionally, each power supply requires three transformers,all rated to the full output load of the power supply.

A third type of dual-input power supply uses relay switching between theinput sources. Relay switching provides high isolation between inputsources but has other disadvantages including difficulty in achieving aclean transfer under all possible fault conditions for AC input sources.

Accordingly, existing approaches to providing redundant input powersources to power systems involve a large increase in system cost or havedrawbacks in switching between input power sources that may limitapplicability in high-reliability power systems.

SUMMARY

Embodiments of the present invention are directed to a dual asymmetricinput power supply architecture for use in power systems employing inputpower source redundancy. The dual asymmetric input power supplyarchitecture maintains the high efficiency of a single-input powersupply while providing an auxiliary connection that may be connected toan auxiliary or secondary input power source. The auxiliary connectionuses the power factor correction and energy storage of the main powerpath from the main power input to avoid duplication of circuits in thepower supply. The dual asymmetric input design meets operational andsafety isolation requirements between the main and auxiliary inputs. Thedual asymmetric input power supply can be designed to start and operatewith either or both inputs connected to input power sources. In the dualasymmetric input power supply architecture, the efficiency of the mainpower path is not degraded by the auxiliary input path, and there is notpossibility of accidentally inhibiting the main input path since it isalways active. Switching from the main input to the auxiliary input canbe done very quickly since there are no large energy storage componentsor mechanical switching devices in the auxiliary path. The dualasymmetric input power supply has the same output power capability andinput fault ride-through capability when operating from either input. Invarious embodiments, the auxiliary input can be an optional feature fora single-input power supply.

According to one aspect consistent with various embodiments, a powerconverter includes a primary power input, an auxiliary power input, anda converter output. A rectifier is coupled to the primary input of thepower converter that provides a rectified voltage at a rectifier output.A converter circuit is coupled to the rectifier output that receives therectified voltage and provides output power at the converter output. Anisolated switching converter circuit is coupled to the auxiliary inputthat provides an auxiliary rectified voltage at the rectifier outputupon detection of a failure condition of the primary input power supplyvoltage.

According to other aspects consistent with various embodiments, thepower converter includes a primary input failure detection circuitcoupled to the primary power input and to the isolated switchingconverter circuit through a galvanically isolated coupling. Thegalvanically isolated coupling may be an optical coupling. The auxiliarycontroller may activate a switching element of the isolated switchingconverter upon detection of the failure condition. The isolatedswitching converter circuit may include a transformer having a primarywinding coupled to the auxiliary power input, a switching elementcoupled to the primary winding of the transformer, and an auxiliarycontroller circuit coupled to the switching element. The converter stagemay include a power factor correction circuit and a switching-modeconverter stage that includes a switching element and a transformerelement.

According to other aspects consistent with various embodiments, a powersystem may include a plurality of power converters, with each powerconverter including an isolated switching converter circuit coupled toan auxiliary input of the power converter that provides a rectifiedvoltage to an input of a power factor correction circuit in the mainpower path upon detection of a failure condition on the primary powerinput. A primary input of a first power converter may be coupled to afirst power source of the power system, and an auxiliary input of thefirst power converter may be coupled to a second power source of thepower system. A primary input of a second power converter may be coupledto the second power source, and an auxiliary input of the second powerconverter may be coupled to the first power source. The first powersource and the second power source may be independent AC power sources.

According to other aspects consistent with various embodiments, a powersystem may include a power converter having an isolated switchingconverter circuit coupled to an auxiliary input of the power converterthat provides a rectified voltage to an input of a power factorcorrection circuit in the main power path upon detection of a failurecondition on the primary power input. A primary input of the powerconverter may be coupled to a primary AC power source of the powersystem, and an auxiliary input of the power converter may be coupled toa an auxiliary DC power source of the power system.

According to other aspects consistent with various embodiments, a powerconverter includes a primary power input, an auxiliary power input, anda converter output. A converter stage is coupled to the rectifier outputthat receives the rectified voltage and provides a DC output voltage atthe converter output. An auxiliary input circuit is coupled to theauxiliary power input and includes a transformer isolated switchingconverter that provides a transformer isolated voltage from theauxiliary power input at the converter input upon detection of a failurecondition of the primary power input. The converter stage may include anactive power factor correction circuit that provides a DC voltage to apower conversion circuit while drawing an input current that issinusoidal and in phase with an AC voltage on the primary power input.The transformer isolated switching converter may include a switchingelement that is activated by an auxiliary control circuit upon detectionof the failure condition of the primary power input. Activating theswitching element may include opening and closing the switching elementat a predetermined frequency. The transformer isolated switchingconverter may include a plurality of switching elements. The pluralityof switching elements may be activated with out-of-phase switchingsignals upon detection of the failure condition of the primary powerinput. According to other aspects consistent with various embodiments, apower converter includes a primary power input and a converter stagecoupled to the primary power input that converts an unregulated inputvoltage at a converter input to a regulated output voltage at a powerconverter output. An auxiliary power input to the power converter isenabled by monitoring the primary power input, detecting a failurecondition of the primary power input, and activating an auxiliaryswitching mode input circuit, in response to detecting the failcondition, to provide a rectified voltage at the converter input fromthe auxiliary power input. Detecting of the failure condition mayinclude comparing a voltage of the primary power input with a threshold,detecting a voltage instability at the primary power input, and/ordetecting a frequency instability at the primary power input. Theauxiliary power input may be monitored such that it can be determinedwhether an auxiliary input power source is connected to the auxiliarypower input before the activating of the auxiliary switching mode inputcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated in referencedfigures of the drawings, in which like numbers refer to like elementsthroughout the description of the figures.

FIG. 1 is a block diagram of a dual asymmetric input power supply unit,according to various embodiments.

FIG. 2 is a circuit diagram of a dual asymmetric input power supplyunit, according to various embodiments.

FIG. 3 illustrates a power system that employs dual asymmetric inputpower supply units, according to various embodiments.

FIG. 4 illustrates a power system that employs single-input power supplyunits, according to various embodiments.

FIG. 5 illustrates a power system that employs dual-input power supplyunits, according to various embodiments.

FIG. 6 illustrates an auxiliary input circuit that may be employed in adual asymmetric input power supply unit, according to variousembodiments.

FIG. 7 illustrates an auxiliary input circuit that may be employed in adual asymmetric input power supply unit, according to variousembodiments.

FIG. 8 illustrates operational waveforms of an auxiliary input circuitthat may be employed in a dual asymmetric input power supply unit,according to various embodiments.

FIG. 9 illustrates a power system that employs aspects of the dualasymmetric input power supply unit architecture, according to variousembodiments.

DETAILED DESCRIPTION

High reliability power supply systems typically have fault tolerantarchitectures that include redundant power supply components. Forexample, a high-reliability power system may include fault tolerance ofthe power supply units (“PSUs”) used in the power system such that thesystem can maintain its full performance capability when any one of thePSUs is out of operation because of component failure or systemmaintenance. In addition, high reliability power systems may include thecapability of operating from more than one independent electrical powersource. For example, a power system may have multiple independent ACinput power sources or a primary AC power source and an AC or DC backuppower source. The power system should be able to operate from one orboth input power sources during normal operation. If one of the inputpower sources fails, the power system should be able to operate from theremaining input power source without disrupting power delivery. It maybe desirable in power systems operating from multiple independent powersources that the output load be shared between the input sources whenboth are present.

Embodiments of the present invention are directed to a dual asymmetricinput power supply architecture for use in power systems employing inputpower source redundancy. The dual asymmetric input power supplyarchitecture maintains the high efficiency of a single-input powersupply while providing an auxiliary connection for input power sourceredundancy. Aspects of the dual asymmetric input power supplyarchitecture provide input power source redundancy at a lower cost andsystem volume than power systems employing single-input or dual-inputpower supplies.

FIG. 1 illustrates a block diagram of a dual asymmetric input PSU 100according to various embodiments. Dual asymmetric input PSU 100 has amain or primary power input 110 and an auxiliary power input 112.Generally, main input 110 is connected to a primary power source (notshown) for dual asymmetric input PSU 100 and auxiliary input 112 isconnected to an auxiliary power source (not shown). When the primarypower source is present at main input 110, dual asymmetric input PSU 100supplies the load power at DC output(s) 120 from the primary powersource through main input 110. In this instance, auxiliary input circuit160 is disabled and dual asymmetric input PSU 100 does not draw powerfrom auxiliary input 112. If the input power source connected to maininput 110 fails or is out of tolerance, dual asymmetric input PSU 100can switch to operating from the auxiliary input power source connectedto auxiliary input 112. Switching from the main input 110 to theauxiliary input 112 in dual asymmetric input PSU 100 can be done veryquickly because there are no large energy storage components ormechanical switching devices in the auxiliary power path.

Commonly, the primary input power source will be an AC power source. TheAC power source connected to main input 110 is filtered with EMI filter130 to provide a filtered AC voltage (V_(F)) 115 at the EMI filteroutput 114. The filtered AC voltage 115 is rectified by bridge rectifier132 to provide rectified voltage (V_(R)) 119 at rectifier output 118.The rectified voltage (V_(R)) 119 is input to power factor correction(“PFC”) module 140 which typically generates a regulated DC voltage(V_(DC)) at the PFC output 142. For example, PFC module 140 may generatea DC voltage in the range of 375-400 VDC with regulation on the order of+/− 10%. Capacitor(s) 144 filters the DC voltage (V_(DC)) at PFC circuitoutput 142 such that it does not vary substantially over the AC cycleperiod of the AC power source connected to main input 110. DC/DCconverter 150 receives the DC voltage (V_(DC)) from PFC output 142 andgenerates one or more regulated DC output voltage(s) and/or current(s)at power supply DC output(s) 120.

If the primary power source connected to main input 110 fails, dualasymmetric input PSU 100 can switch to an auxiliary power sourceconnected to auxiliary input 112 without interrupting the output powerat DC output(s) 120. Specifically, auxiliary input circuit 160 isenabled and supplies power from auxiliary input 112 to the input 118 ofPFC circuit 140 when a failure condition is detected for the main input110. In this instance, PFC circuit 140 and DC/DC converter 150 operatenormally using power supplied from auxiliary input 112 through auxiliaryinput circuit 160. Auxiliary input circuit 160 can be rapidly enabledsuch that the power delivery to the input of PFC circuit 140 is notsubstantially interrupted. In this way, the power output of dualasymmetric input PSU 100 through PFC circuit 140 and DC/DC converter 150is not interrupted when the input source connected to main AC input 110fails. In various embodiments, auxiliary input circuit 160 may accept anAC voltage, high-voltage DC, or low-voltage DC power input at auxiliaryinput 112.

In some exemplary embodiments, dual asymmetric input PSU 100 includesinput fail detection circuit 170 that indicates a failure condition ofmain input 110 to auxiliary input circuit 160 through galvanicallyisolated coupling 172. Galvanically isolated coupling 172 allows inputfail detection circuit 170 to provide a signal indicating whether theinput power source connected to main input 110 is within or outside oftolerance to auxiliary input circuit 160 while maintaining isolationbetween main input 110 and auxiliary input 112. For example,galvanically isolated coupling 172 allows input fail detection circuitto provide a signal indicating whether main input 110 is presentregardless of voltage reference, voltage amplitude, frequency, and/orphase differences between main input 110 and auxiliary input 112.Galvanically isolated coupling 172 may be, for example, an opticalcoupling.

FIG. 2 illustrates a circuit diagram of one embodiment of a dualasymmetric input PSU 100 a in more detail. As illustrated in FIG. 2,main input 110 of dual asymmetric input PSU 100 a is connected to PFCcircuit 140 a through EMI filter 130 and bridge rectifier 132.Generally, main input 110 will be connected to an AC input power source.PFC circuit 140 a may be any suitable active or passive PFC circuit thatmakes the AC input current waveform of dual asymmetric input PSU 100 asinusoidal and in phase with the AC input voltage of an AC input powersource. As shown in FIG. 2, PFC circuit 140 a is a boost (or step-up)converter that includes inductor 241, PFC controller 242, switchingelement 243, diode 245, and bypass or bulk capacitor 244. However, othersuitable active or passive PFC topologies may also be used. For example,PFC circuit 140 a may be another non-transformer isolated switchingpower supply topology such as a buck or buck/boost converter topology.

DC/DC converter 150 a of dual asymmetric input PSU 100 a may be anysuitable DC/DC converter(s) that supplies power at regulated outputvoltage(s) and/or current(s) from the DC output of PFC circuit 140 a. Asillustrated in FIG. 2, DC/DC converter 150 a of dual asymmetric inputPSU 100 a includes switching-mode power conversion circuits that supplypower at multiple output voltages. However, DC/DC converter 150 a may beany DC/DC converter topology that supplies and regulates voltage(s)and/or current(s) at DC power output(s) 120 of dual asymmetric input PSU100 a. In various embodiments, PFC circuit 140 a and DC/DC converter 150a may be combined into one or more switching mode power converters. Forexample, PFC circuit 140 a and DC/DC converter 150 a may be replaced bya single-stage converter circuit that provides regulated outputvoltage(s) and/or current(s) at DC power output(s) 120.

As illustrated in FIG. 2, auxiliary input circuit 160 a includes atransformer isolated switching converter that drives the input of PFCcircuit 140 a from auxiliary input 112 when a fail condition is detectedon main input 110. The transformer isolated switching converter ofauxiliary input circuit 160 a includes controller 262, transformer 263,switching transistor 264, and output diode 265. Auxiliary input circuit160 a may supply power from an auxiliary AC or high-voltage DC powersource. The ratio of number of turns in the secondary winding (N(S))compared to the number of turns in the primary winding (N(P)) (i.e.,turns ratio) for transformer 263 may be adjusted to provide a suitablevoltage for input to PFC circuit 140 a from the auxiliary input 112. Forexample, a turns ratio of 1:1 for transformer 263 provides approximatelyequal input and output voltages of auxiliary input circuit 160 a. Inthis instance, auxiliary input circuit 160 a could accept either an ACinput voltage in the 100 VAC to 240 VAC range or a DC input in the 140VDC to 340 VDC range. A different turns ratio for transformer 263 couldbe used to provide a different auxiliary AC or DC input voltage range.

The transformer isolated switching converter of auxiliary input circuit160 a provides isolation between auxiliary input 112 and main input 110of dual asymmetric input PSU 100 a. Specifically, main input 110 andauxiliary input 112 are isolated from each other by transformer 263 ofauxiliary input circuit 160 a. When auxiliary input 112 is unplugged,power does not feed back from main input 110 through transformer 263 toauxiliary input 112. When dual asymmetric input PSU 100 a is operatingfrom auxiliary input 112, circuits connected to main input 110 becomesecondary circuits isolated from the auxiliary input power sourceconnected to auxiliary input 112. While these circuits are isolated fromthe auxiliary input source, hazardous voltage should also be preventedfrom feeding back from auxiliary input 112 to main input 110. Bridgerectifier 130 prevents the rectified voltage 118 from appearing at maininput 110. Main input 110 and auxiliary input 112 will meet the UL/EN60950 safety standard requirements for operator accessible limitedcurrent circuits including the test with a single failure of anycomponent.

As illustrated in FIG. 2, the transformer isolated switching converterof auxiliary input circuit 160 a is a forward-mode converter. However,other transformer isolated switching converter topologies may be used inauxiliary input circuit 160 a. For example, flyback, push-pull,half-bridge, or full-bridge converter topologies may be used in variousembodiments.

Still referring to FIG. 2, the operation of dual asymmetric input PSU100 a is described in more detail. The main power path supplying powerfrom main input 110 to PFC circuit 140 a and DC/DC converter 150 a isalways active. Therefore, there is no possibility that the main powerpath will be disabled. Typically, when the primary power sourceconnected to main input 110 is present, auxiliary input circuit 160 a isdisabled. For example, controller 262 disables auxiliary input circuit160 a by driving transistor 264 to an off or open state. When transistor264 is maintained in an off state, no current flows through transformer263 and auxiliary input circuit 160 a will not supply a voltage to theinput 118 of PFC circuit 140 a. With auxiliary input circuit 160 adisabled, the efficiency of dual asymmetric input PSU 100 a is notdegraded by the presence of auxiliary input circuit 160 a.

Input fail detection circuit 170 monitors the voltage on main input 110,e.g., by monitoring the voltage 114 at the output of the EMI filter 130.If input fail detection circuit 170 detects a fail condition, itnotifies auxiliary input circuit 160 a by way of optical coupling 271,which is received by auxiliary input circuit 160 a at optical couplingsensor 261. Input fail detection circuit 170 includes circuits formonitoring main input 110 and detecting failure conditions. Failureconditions of main input 110 detected by input fail detection circuit170 may include an out of tolerance voltage range, frequencyfluctuations, and/or other failure conditions.

Controller 262 receives the notification indicating a failure on maininput 110 and can enable auxiliary input circuit 160 a by drivingtransistor 264 with an appropriate switching signal to supply power tothe input 118 of PFC circuit 140. The switching signal to transistor 264is generally a higher frequency than the typical line frequency of 50-60Hz. For example, controller 262 may drive transistor 264 with a signalthat switches at a frequency in the range of 10-100 KHz.

Dual asymmetric input PSU 100 a operates in a similar manner to adual-input power supply with input relay switching, but the input sourceswitching is much faster and the dual-asymmetric input PSU is able tooperate simultaneously from both inputs without problems. Main input 110is used when both inputs are present because it has the higherefficiency power path. When a problem is detected on main input 110,auxiliary input circuit 160 a can be enabled to provide power fromauxiliary input 112 fast enough to maintain the power output at DCoutput(s) 120. For example, auxiliary input circuit 160 a may be enabledin less than one millisecond. Bulk capacitor 244 typically maintainsenough charge that no disruption of power at DC output(s) 120 occurswhen the primary input source fails and auxiliary input circuit 160 a isenabled. False alarms are not a problem because auxiliary input circuit160 a can be turned on and off at any time even while the main input 110is present. The only effects of cycling the auxiliary input aretemporary loss of efficiency and a possible reduction in power factorwhen operating from two independent AC input sources. When the outputpower of dual asymmetric input PSU 100 a is supplied from auxiliaryinput 112, the efficiency of the power supply is lower by about 5%because of the additional transformer in the power path of auxiliaryinput circuit 160 a.

In embodiments, dual asymmetric input PSU 100 a monitors auxiliary input112 and uses information about both main input 110 and auxiliary input112 to determine when to enable the power path from auxiliary input 112.In one embodiment, dual asymmetric input PSU 100 a only enables thepower path through auxiliary input circuit 160 a when a sufficientvoltage is present on auxiliary input 112 to supply the required poweroutput for dual asymmetric input PSU 100 a. In another embodiment, dualasymmetric input PSU 100 a evaluates whether main input 110 or auxiliaryinput 112 should be used based on voltage, frequency, and/or phase ofmain input 110 and auxiliary input 112. Dual asymmetric input PSU 100 athen enables auxiliary input circuit 160 a if auxiliary input 112 is thepreferred input power source. In these embodiments, input fail detectioncircuit 170 may monitor both main input 110 and auxiliary input 112,providing an enable signal to controller 262 when the auxiliary powerpath from auxiliary input 112 should supply power instead of the mainpower path from main input 110.

In some exemplary embodiments, dual asymmetric input PSU 100 a mayanalyze the voltage, frequency, and/or phase of main input 110 topredict an imminent failure of main input 110 and determine anappropriate time to enable auxiliary input circuit 160 a. For example,dual asymmetric input PSU 100 a may compare the voltage on main input110 with a threshold to determine if the main power supply is present.Alternatively, dual asymmetric input PSU 100 a may detect a voltageand/or frequency instability on main input 110 to determine if failureof main input 110 is imminent. In embodiments, dual asymmetric input PSU100 a predicts an imminent failure of the primary input power sourceconnected to main input 110 and enables auxiliary input circuit 160 a tosupply power to PFC circuit 140 a from auxiliary input 112 before theprimary input power source fails.

In FIG. 2, switching elements including transistors 243 and 264 areillustrated as metal oxide semiconductor field effect transistors(“MOSFETs”). However, any suitable switching element may be used for theswitching elements of dual asymmetric input PSU 100 a. For example,other suitable switching elements include bipolar junction transistors(“BJTs”), junction gate field-effect transistors (“JFETs”), insulatedgate bipolar transistor (“IGBTs”), and/or other common switchingelements. Circuit design and implementation of PFC controller 242, inputfail detection circuit 170, controller 262, and the circuit blocks thatmake up DC/DC converter 150 a are within the knowledge of those of skillin the art, and need not be described further herein. These circuits maybe a combination of integrated and discrete circuit components such asapplication specific integrated circuits (“ASICs”), transistors,capacitors, resistors, inductors, or the like.

FIG. 3 illustrates power system 300 that employs dual asymmetric inputPSUs to provide PSU redundancy and/or input power source redundancyaccording to various embodiments described herein. In power system 300,dual asymmetric input PSUs 302 and 304 have main inputs connected toinput power source A 310 and auxiliary inputs connected to input powersource B 312. Dual asymmetric input PSUs 306 and 308 have main inputsconnected to input power source B 312 and auxiliary inputs connected toinput power source A 310. Therefore, if both input power source A 310and input power source B 312 are present, power supplies 302 and 304supply approximately half of the load power at DC output(s) 320 throughtheir main power paths from input power source A and power supplies 306and 308 supply the remainder of the load power through their main powerpaths from input source B 312. While power system 300 is typical of apower system with two independent AC input sources, input power source A310 and input power source B 312 may be AC or DC input power sources.

In one embodiment, power system 300 employs an N+1 redundantconfiguration providing PSU redundancy and input power sourceredundancy. For example, if each dual asymmetric input PSU 302, 304,306, and 308 can supply 3000 watts, power system 300 can support a loadof 9000 watts with both PSU redundancy and input power sourceredundancy. If one dual asymmetric input PSU of power system 300 fails,the remaining PSUs can still supply the rated power through theremaining power supplies. In this instance, the fault condition istolerated without interruption of output power at DC output(s) 320.

Similarly, if one of input power source A 310 or input power source B312 fails, power system 300 can still supply the rated power from theremaining input power source. For example, if input power source A 310fails, dual asymmetric input PSUs 302 and 304 switch over to theirauxiliary inputs and supply power to DC output(s) 320 from input powersource B 312. In this instance, output power is supplied by power system300 at DC output(s) 320 from dual asymmetric input PSUs 306 and 308through their main power paths and from dual asymmetric input PSUs 302and 304 through their auxiliary power paths. Dual asymmetric input PSUs302 and 304 have slightly reduced efficiency because they are operatingthrough their auxiliary power paths to supply power from input powersource B 312.

While FIG. 3 illustrates power system 300 including four dual asymmetricinput PSUs in a 3+1 redundant configuration with PSU redundancy andinput power source redundancy, dual asymmetric input PSUs may be used invarious other configurations to provide PSU redundancy and/or inputpower source redundancy in a power system. For example, dual asymmetricinput PSUs may be used in an N+1 configuration to provide PSU redundancyand/or input power source redundancy for any value of N, including N=1,N=2, N=3, N=4, and so on.

In another embodiment, a power system with an AC primary power sourceand a DC backup power source may use dual asymmetric input PSUs toprovide PSU and/or input power source redundancy. In this instance, theAC primary power source is connected to the main inputs of each dualasymmetric input PSU while the DC backup power source is connected tothe auxiliary inputs of each dual asymmetric input PSU. When the ACprimary power source is present, the dual asymmetric input PSUs operatefrom the AC primary power source. The DC backup power source may bepresent and ready to provide power if the AC primary power source fails.However, the dual asymmetric PSUs will not draw power from the DC backuppower source until the AC primary source fails. If the AC primary powersource does fail, the dual asymmetric input PSUs will switch over to theDC backup power source and continue to supply the rated power at the DCoutput load from the DC backup power source.

In various configurations, power systems employing dual asymmetric inputPSUs have significant advantages over previous known methods ofproviding power supply and/or input power source redundancy in terms ofsystem cost and volume. One previous method of providing input powersource redundancy is an N+N single-input PSU configuration. FIG. 4illustrates a power system 400 employing single-input PSUs configured inan N+N redundant system. In power system 400, single-input PSUs 432,434, and 436 are connected to input power source A 410 whilesingle-input PSUs 442, 444, and 446 are connected to input power sourceB 412. In power system 400, each component of the single-input PSUs isduplicated in the N+N single-input PSU redundant architecture. Notably,the N+N single-input PSU redundant architecture of power system 400provides only input redundancy or PSU redundancy and not both types ofredundancy. This means that the N+N single-input PSU architecture is nottolerant of an input failure and a PSU failure at the same time.

A comparison of the N+N single-input PSU redundant architecture forproviding input source redundancy to the N+1 dual asymmetric input PSUredundant architecture illustrates the advantages in cost and powersystem volume of systems employing dual asymmetric input PSUs. Thefollowing table estimates the reduction in power system product volumeusing an N+1 dual asymmetric input PSU architecture when compared to anN+N single-input PSU architecture for a total power supply load of 5000watts. The table assumes that a single-input PSU achieves a powerdensity of 25 W/in³ and that a dual asymmetric input PSU has a 30%increase in PSU volume (estimates range from 25% to 30% for current PSUcircuit topologies). As can be seen, the power supply volume reductionusing dual asymmetric input PSUs becomes larger and larger as Nincreases.

N + 1 dual N + N single-input PSU asymmetric input PSU ConfigurationConfiguration Total Total PSU System PSU System Volume Total RatingVolume Total Rating Volume Change N PSUs (Watts) (in³) PSUs (Watts)(in³) (%) 1 2 5000 400 2 5000 520.0 30 2 4 2500 400 3 2500 390.0 −2.5 36 1666.7 400 4 1666.7 346.7 −13.3 4 8 1250 400 5 1250 325.0 −18.8 5 101000 400 6 1000 312.0 −22.0 6 12 833.3 400 7 833.3 303.3 −24.2 7 14714.3 400 8 714.3 297.1 −25.7

Another previous method of providing input power source redundancy inpower systems is to use dual-input PSUs with transformer isolation ofthe inputs within or directly after the PFC stage. FIG. 5 illustrates apower system 500 that employs dual-input PSUs and provides input powersource and PSU redundancy with an N+1 redundant architecture. In powersystem 500, each PSU 502, 504, 506 has two transformer-isolated PFCcircuits 532 feeding one DC/DC converter stage 150. This approach avoidsduplication of the DC/DC conversion stage but reduces efficiency of thepower supply operating from either and/or both power supply inputs byabout 5% because of the additional transformer in each power supplypath. Additionally, each dual-input PSU has three transformers, eachrated for the full output power of the PSU. As a result, the dual-inputPSU does not offer significant cost or system volume advantages over thesingle-input PSU N+N redundant architecture and reduces power systemefficiency under normal operating conditions.

As discussed above, power systems may use a variety of back-up powersources. These sources include independent AC input sources, generators,and/or battery-back up uninterruptible power supplies (“UPSs”).Auxiliary input circuit 160 of dual asymmetric input PSU 100 may bedesigned to accept an AC voltage, high-voltage DC, and/or low-voltage DCauxiliary power source to support a variety of independent or back-uppower sources.

FIG. 6 illustrates an alternative auxiliary input circuit 160 b that maybe employed in dual asymmetric input PSU 100 for supplying power from ahigh-voltage DC or low-voltage DC input power source according tovarious exemplary embodiments. Auxiliary input circuit 160 b includestransformer 663, transistor 664, auxiliary input controller 662, andoutput diode 665. Auxiliary input controller 662 receives auxiliarycontrol input 666 that indicates whether the input source of main ACinput 110 is present. For example, auxiliary control input may come froman input fail detection circuit, such as input fail detection circuit170 of dual asymmetric input PSU 100 through galvanically isolatedcoupling 172. When the primary power source connected to main input 110of dual asymmetric input PSU 100 is present, auxiliary input circuit 160b is disabled, which means that controller 662 drives the transistor 664to an off state. In this instance, auxiliary input circuit 160 b doesnot provide power at output 680 to the input 118 of PFC circuit 140 ofdual asymmetric input PSU 100. If auxiliary control input 666 ofauxiliary input circuit 160 b indicates that the main input 110 of dualasymmetric input PSU 100 has failed or is out of tolerance, auxiliaryinput controller 662 enables auxiliary input circuit 160 b by switchingtransistor 664 at an appropriate switching frequency. For example,auxiliary input controller may switch transistor 664 at a switchingfrequency in the range of 10-100 KHz. In one embodiment, transistor 664is switched at approximately 50 KHz. In this instance, auxiliary inputcircuit supplies power at output 680 to the input 118 of PFC circuit 140from the DC power source connected to auxiliary input 612. Auxiliaryinput circuit 160 b may include EMI filter 630 to filter auxiliary input612.

In auxiliary input circuit 160 b, the turns ratio (N(P):N(S)) oftransformer 663 may be changed to provide for a different range of DCinput voltages. A lower turns ratio may be used for higher voltage DCinput sources. For example, a turns ratio of 1:1 may be acceptable forhigh-voltage DC input sources in the range of 140 VDC to 340 VDC. For alower DC input voltage range, a higher turns ratio may be used. Forexample, for auxiliary input circuit 160 b to accept a 48 VDC nominalinput voltage on auxiliary input 612, a turns ratio of 1:4 may be used.Typically, auxiliary input circuit 160 b can accept a wide range of DCvoltage variation on auxiliary input 612 and still supply the ratedpower of dual asymmetric input PSU 100 from auxiliary input 612. Forexample, the range of maximum accepted voltage to minimum acceptedvoltage may be approximately a factor of 3 to 1.

FIG. 7 illustrates an alternative auxiliary input circuit 160 c that maybe employed in dual asymmetric input PSU 100 for supplying power from ACor DC voltage sources. Auxiliary input circuit 160 c includestransformer 763, transistors 764 and 765, auxiliary input controller762, and output diodes 767 and 768. Auxiliary input controller 762receives auxiliary control input 766 that indicates whether the primaryinput source connected to main input 110 is present. For example,auxiliary control input 766 may come from input fail detection circuit170 of dual asymmetric input PSU 100 through galvanically isolatedcoupling 172. When the primary input source connected to main input 110of dual asymmetric input PSU 100 is present, auxiliary input circuit 160c is disabled, meaning that auxiliary input circuit 160 c does notprovide power to the input 118 of PFC circuit 140. If auxiliary controlinput 766 of auxiliary input circuit 160 c indicates that the primaryinput source connected to main input 110 of dual asymmetric input PSU100 has failed or is out of tolerance, auxiliary input controller 762enables auxiliary input circuit 160 c such that it supplies power to theinput 118 of PFC circuit 140 from the input power source connected toauxiliary input 712.

When auxiliary input circuit 160 c is enabled to supply power fromauxiliary input voltage 712, transistors 764 and 765 are driven without-of-phase square wave signals by controller 762. FIG. 8 illustratesdrive waveforms that may be used to drive transistors 764 and 765, andthe resulting voltage at output 780 of auxiliary input circuit 160 cwhen it is enabled via auxiliary control input 766. In FIG. 8, waveform802 shows the voltage of an AC input source connected to auxiliary input712 of auxiliary input circuit 160 c. Waveforms 804 and 806 illustrateout-of-phase drive control signals for switching transistors 764 and765, respectively. For ease of understanding, the time scale ofwaveforms 804 and 806 in FIG. 8 is not illustrated to scale compared tothe time scale of AC input voltage waveform 802. For example, theswitching frequency of transistors 764 and 765 may be 10-100 KHz range,while the line frequency of the AC input source illustrated by waveform802 may be 50-60 Hz. In one embodiment, transistors 764 and 765 areswitched at approximately 50 KHz. Additionally, while waveforms 804 and806 illustrate only out-of-phase square wave signals, in practice,transistors 764 and 765 may be driven by non-overlapping drivewaveforms, which means that for each cycle one transistor is not turnedon until a short time after the other transistor has been turned off.

Waveforms 808 and 810 illustrate the voltage that would be present atthe cathodes of diodes D1 (767) and D2 (768) if the cathodes were notconnected together. As described above, the time scale of switching ofwaveforms 808 and 810 is not shown to scale as compared to the timescale of AC input waveform 802. With diodes D1 (767) and D2 (768)connected together, the resulting voltage at output 780 of auxiliaryinput circuit 160 c is illustrated by waveform 812. In practice,waveform 812 may have a slight ripple due to switching waveforms 804 and806. However, this ripple may be smoothed by the small (˜1 uF) bypasscapacitors typically present on input 118 to PFC circuit 140.

Referring back to FIG. 1, aspects of dual asymmetric input PSU 100 maybe used to provide modular power systems that provide redundancy withrespect to PSU's or input power sources. For example, auxiliary inputcircuit 160 could be in a separate enclosure that plugs into, or isconnected by power cables, to a single-input PSU with an auxiliary inputto the PFC.

FIG. 9 illustrates power system 900 that employs aspects of the dualasymmetric PSU architecture described above. In power system 900,auxiliary input module 904 provides a redundant input power path tosingle-input PSU 902. Single-input PSU 902 has PFC input port 918 toallow single-input PSU 902 to accept input power from an auxiliarysource. Auxiliary input module 904 includes auxiliary input circuit 960that accepts auxiliary control input 966. Auxiliary input circuit 960may accept an AC voltage, high-voltage DC, and/or low-voltage DCauxiliary input power source at auxiliary input 912. For example,auxiliary input circuit 960 may be one of auxiliary input circuit 160 a,160 b, or 160 c, as described above.

Auxiliary input module 904 adds input power source redundancy to powersystem 900 with lower additional cost than a redundant single-input PSU.When the power source connected to input 910 of single-input PSU 902 ispresent, auxiliary input circuit 960 is disabled and single-input PSU902 provides power to DC output(s) 920 from the power source connectedto input 910. If a fail condition of the input power source connected toinput 910 is detected by input fail detection circuit 970, input faildetection circuit 970 indicates the failure condition to auxiliary inputcircuit 960 of auxiliary input module 904 through a galvanicallyisolated coupling. As illustrated in FIG. 9, the galvanically isolatedcoupling includes optical coupling emitter 974 and optical couplingreceiver 964. In auxiliary input module 904, auxiliary input circuit 960of auxiliary input module 904 receives the indicator through auxiliarycontrol input 966 and provides power to PFC input connection 918 fromauxiliary input 912 through module output 968. In embodiments, inputfail detection circuit 970 may be located outside of single-input PSU902. For example, input fail detection circuit 970 may be located inauxiliary input module 904. In this instance, the power supply connectedto input 910 of single-input PSU 902 is also connected to an input ofauxiliary input module 904. Alternatively, input fail detection circuit970 may be located in third module that is separate from single-inputPSU 902 and auxiliary input module 904. For example, in a power systemwith multiple single-input PSUs 902 and multiple auxiliary input modules904, a single input fail detection module may monitor the primary inputpower source connected to the main inputs 910 of the single-input PSUs902 and enable the auxiliary input modules 904 to provide power from oneor more auxiliary power sources connected to auxiliary input 912 ofauxiliary input modules 904.

Various other power system configurations may be created using themodules of power system 900. For example, more than one auxiliary inputcircuit 904 may have outputs 968 connected to one single-input PSU 902to provide multiple redundancy of the input power source. In this way,multiple AC or DC auxiliary or backup power sources could be availableif the primary power source connected to the main input 910 of thesingle-input PSU 902 fails.

The foregoing description has been presented for purposes ofillustration and description. Furthermore, the description is notintended to limit embodiments of the invention to the form disclosedherein. While a number of exemplary aspects and embodiments have beendiscussed above, those of skill in the art will recognize certainvariations, modifications, permutations, additions, and sub-combinationsthereof.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor.

The various illustrative logical blocks, modules, and circuits describedmay be implemented or performed with a general purpose processor, adigital signal processor (DSP), an ASIC, a field programmable gate arraysignal (FPGA), or other programmable logic device (PLD), discrete gate,or transistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A generalpurpose processor may be a microprocessor, but in the alternative, theprocessor may be any commercially available processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure, may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of tangible storage medium. Someexamples of storage media that may be used include random access memory(RAM), read only memory (ROM), flash memory, EPROM memory, EEPROMmemory, registers, a hard disk, a removable disk, a CD-ROM and so forth.A storage medium may be coupled to a processor such that the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.A software module may be a single instruction, or many instructions, andmay be distributed over several different code segments, among differentprograms, and across multiple storage media.

The methods disclosed herein comprise one or more actions for achievingthe described method. The method and/or actions may be interchanged withone another without departing from the scope of the claims. In otherwords, unless a specific order of actions is specified, the order and/oruse of specific actions may be modified without departing from the scopeof the claims.

The functions described may be implemented in hardware, software,firmware, or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on a tangiblecomputer-readable medium. A storage medium may be any available tangiblemedium that can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM, or other optical disk storage, magnetic disk storage, or othermagnetic storage devices, or any other tangible medium that can be usedto carry or store desired program code in the form of instructions ordata structures and that can be accessed by a computer. Disk and disc,as used herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs usually reproduce dataoptically with lasers.

Thus, a computer program product may perform operations presentedherein. For example, such a computer program product may be a computerreadable tangible medium having instructions tangibly stored (and/orencoded) thereon, the instructions being executable by one or moreprocessors to perform the operations described herein. The computerprogram product may include packaging material.

Software or instructions may also be transmitted over a transmissionmedium. For example, software may be transmitted from a website, server,or other remote source using a transmission medium such as a coaxialcable, fiber optic cable, twisted pair, digital subscriber line (DSL),or wireless technology such as infrared, radio, or microwave.

Further, modules and/or other appropriate means for performing themethods and techniques described herein can be downloaded and/orotherwise obtained by a user terminal and/or base station as applicable.For example, such a device can be coupled to a server to facilitate thetransfer of means for performing the methods described herein.Alternatively, various methods described herein can be provided viastorage means (e.g., RAM, ROM, a physical storage medium such as a CD orfloppy disk, etc.), such that a user terminal and/or base station canobtain the various methods upon coupling or providing the storage meansto the device. Moreover, any other suitable technique for providing themethods and techniques described herein to a device can be utilized.

Other examples and implementations are within the scope and spirit ofthe disclosure and appended claims. For example, due to the nature ofsoftware, functions described above can be implemented using softwareexecuted by a processor, hardware, firmware, hardwiring, or combinationsof any of these. Features implementing functions may also be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations.Also, as used herein, including in the claims, “or” as used in a list ofitems prefaced by “at least one of” indicates a disjunctive list suchthat, for example, a list of “at least one of A, B, or C” means A or Bor C or AB or AC or BC or ABC (i.e., A and B and C). Further, the term“exemplary” does not mean that the described example is preferred orbetter than other examples.

Various changes, substitutions, and alterations to the techniquesdescribed herein can be made without departing from the technology ofthe teachings as defined by the appended claims. Moreover, the scope ofthe disclosure and claims is not limited to the particular aspects ofthe process, machine, manufacture, composition of matter, means,methods, and actions described above. Processes, machines, manufacture,compositions of matter, means, methods, or actions, presently existingor later to be developed, that perform substantially the same functionor achieve substantially the same result as the corresponding aspectsdescribed herein may be utilized. Accordingly, the appended claimsinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or actions

What is claimed is:
 1. A method of enabling an auxiliary power input to a power converter, the power converter including a primary power input and a converter stage coupled to the primary power input that converts an unregulated input voltage at a power factor correction (PFC) input to a regulated output voltage at a power converter output, the method comprising: monitoring the primary power input; detecting a failure condition of the primary power input; and activating an auxiliary switching mode input circuit, in response to detecting the failure condition, to provide a rectified voltage at the PFC input from the auxiliary power input, the auxiliary switching mode input circuit being transformer-isolated from the PFC input.
 2. The method of claim 1, wherein the detecting of the failure condition includes comparing a voltage of the primary power input with a threshold.
 3. The method of claim 1, wherein the detecting of the failure condition includes detecting a voltage instability at the primary power input.
 4. The method of claim 1, wherein the detecting of the failure condition includes detecting a frequency instability at the primary power input.
 5. The method of claim 1, further including monitoring the auxiliary power input and determining that an auxiliary input power source is connected to the auxiliary power input before the activating of the auxiliary switching mode input circuit. 